I have two published apps (shared) written in Xamarin using VS 2017 and decided to upgrade to 2019 as it is supposedly stable. Android no longer compiles and all the System modules under references are crossed out. This includes System, System.Core, System.Xml, System.Xml.Linq with error message "Assembly not found for Xamarin.Android v9.0 support". Tried changing to V8.1, V8.0 nada.
I reverted back to 2017 with time machine backups but problem persists. Any ideas of where to look next will be much appreciated.
To be sure I also reverted to my latest working git copy of the project. Still no luck.